This invention relates to a new technique for transmitting the horizontally and vertically polarized signals of a polarization diverse antenna over fiber optics.
The invention simplifies signal transmission between a source such as a communication antenna and a polarization diversity receiver such as the signal processor at a node of a cellular communication system. For example, an RF polarization diversity receiver is used to overcome fading associated with multipath transmission encountered in a cellular network. Conventionally, either two coax transmission lines or two fiber optic links are used to transmit the two differently polarized signals from the antenna to the signal processor at the node. The need for two transmission lines increases system cost. Alternately, one of the polarized signals at the antenna could be frequency shifted with respect to the other so that the signals become frequency multiplexed and can thus be transmitted over a single transmission line. Such frequency division multiplexing approach is widely used in modern telephone system as discussed in "Transmission Systems for Communication" by Members of the Technical Staff, Bell Telephone Laboratories, Bell Telephone Laboratories, Inc. 1970, pages 124-139. This system requires complex frequency shifting electronics at both ends of the transmission line.
It would therefore be advantageous to provide a single fiber optic link between the source and the receiver without using complex frequency shifting electronics and with no interference between the signals.
It would further be advantageous to provide an inexpensive antenna remoting system for cellular telephones.